Focusing device comprising a plurality of scatterers and beam scanner and scope device

ABSTRACT

Provided is a focusing device that includes a substrate and a plurality of scatterers provided at both sides of the substrate. The scatterers on the both sides of the focusing device may correct geometric aberration, and thus, a field of view (FOV) of the focusing device may be widened.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part application of U.S. patentapplication Ser. No. 15/987,090, filed on May 23, 2018, which is acontinuation of application Ser. No. 15/093,987, filed on Apr. 8, 2016,now U.S. Pat. No. 995,930, issued on Jun. 12, 2018, which claims thebenefit of U.S. Provisional Patent Application 62/144,750, filed on Apr.8, 2015, in the U.S. Patent and Trademark Office, and Korean PatentApplication No. 10-2016-0014992, filed on Feb. 5, 2016, in the KoreanIntellectual Property Office, the disclosures of which are incorporatedherein in their entireties by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No.W911NF-14-1-0345 awarded by the U.S. Army. The government has certainrights in the invention.

BACKGROUND 1. Field

Apparatuses and methods consistent with the present disclosure relate toa focusing device, and a beam scanner and a scope device that use thefocusing device as an optical path modifier.

2. Description of the Related Art

Optical sensors using semiconductor-based sensor arrays are widely usedin mobile devices, wearable devices, and the Internet of Things (IoT).Although size reduction of the aforementioned devices is desired, it isdifficult to reduce the thickness of focusing devices in theaforementioned devices.

Also, due to the increased use of 3-dimensional (3D) image sensors inthe IoT, gaming devices, and other mobile devices, focusing devices foradjusting a path of light incident on the 3D image sensors are required.However, the fields of view of the focusing devices may be limited bycoma aberration of the focusing devices. Thus, research has beenconducted to combine a plurality of optical lenses and thus remove comaaberration. However, since a substantial amount of space is necessary tocombine a plurality of optical lenses, it is difficult to reduce thesize of the focusing devices.

SUMMARY

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented exemplary embodiments.

According to an aspect of an exemplary embodiment, a focusing deviceincludes a substrate; a first thin lens provided at a first surface ofthe substrate and comprising a plurality of first scatterers; and asecond thin lens provided at a second surface of the substrate andcomprising a plurality of second scatterers. The first scatterers of thefirst thin lens are configured to correct geometric aberration (fieldcurvature, coma aberration, astigmatism, etc.) of the second thin lens.

The first and second thin lenses may be configured to allow light toform a focusing point on a focal plane regardless of an angle at whichlight is incident on the first surface.

A phase shift of light that passes through the second scatterers maydecrease from a central area of the second thin lens to a peripheralarea of the second thin lens.

A phase shift of light that passes through the first scatterers maydecrease from a peripheral area of the first thin lens to a middle areaof the first thin lens and increases again from the middle area of thefirst thin lens to a central area of the first thin lens.

The first and second thin lenses may be configured to change a locationat which light is focused on the focal plane according to the angle atwhich the light is incident on the first surface.

The first and second thin lenses area configured to determine thelocation at which the light may be focused on the focal plane accordingto Equation 1:h=f*tan θ

wherein ‘h’ is a distance between the location of the focusing point andan optical axis of the focusing device, ‘f’ is an effective focal lengthof the focusing device, and ‘θ’ is the incident angle of light.

Respective refractive indexes of the first and second scatterers may begreater than a refractive index of the substrate.

The substrate may include at least one selected from glass (fusedsilica, BK7, etc.), quartz, polymer (PMMA, SU-8, etc.) and plastic, andthe first and second scatterers comprise at least one selected fromcrystalline silicon (c-Si), polycrystalline silicon (poly Si), amorphoussilicon (a-Si), and group III-V compound semiconductors (GaP, GAN, GaAs,etc.), SiC, TiO₂, and SiN.

The first and second scatterers may be configured to allow incidentlight within a wavelength band to form a focusing point on a focalplane.

Distances between the first scatterers and distances between the secondscatterers may be less than wavelengths in the wavelength band.

Respective heights of the first scatterers and respective heights of thesecond scatterers may be less than wavelengths in the wavelength band.

The focusing device may further include an optical filter configured toblock the incident light of wavelengths of outside the wavelength band.

At least one of respective shapes of the first and second scatterers andrespective sizes of the first and second scatterers may change accordingto a thickness of the substrate.

Each of the first and second scatterers may have at least one of acylindrical shape, a cylindroid shape, and a polyhedral pillar shape.

According to another aspect of an exemplary embodiment, a beam scannerincludes an optical path modifier comprising a substrate, a first thinlens provided at a first surface of the substrate and comprising aplurality of first scatterers, and a second thin lens provided at asecond surface of the substrate and comprising a plurality of secondscatterers; and a light source array spaced apart from the secondsurface of the substrate and comprising a plurality of light sources.The first scatterers of the first thin lens are configured to correctcoma aberration of the second thin lens.

The optical path modifier may change path of light emitted from thelight sources according to respective locations of the light sources.

The optical path modifier may modify light emitted from one of the lightsources into parallel rays.

According to another aspect of an exemplary embodiment, a scope deviceincludes an object lens unit comprising a substrate; a first thin lensprovided at a first surface of the substrate and comprising a pluralityof first scatterers, and a second thin lens provided at a second surfaceof the substrate and comprising a plurality of second scatterers; and alight source facing the second surface of the substrate and configuredto emit light on a target object. The first scatterers of the first thinlens are configured to correct coma aberration of the second thin lens.

Light emitted by the light source may have at least two wavelengths withdifferent transmission rates with respect to the target object.

The light emitted by the light source may be scattered at differentlocations by the target object according to wavelengths of the lightemitted by the light source. The object lens unit may be configured tochange a path of the light according to the locations at which the lightis scattered by the target object.

According to another aspect of an exemplary embodiment, a focusingdevice with respect to light of predetermined wavelength band includes:a substrate; a first thin lens provided at a first surface of thesubstrate and comprising a plurality of first scatterers; and a secondthin lens provided at a second surface of the substrate and comprising aplurality of second scatterers, wherein the plurality of firstscatterers of the first thin lens are configured to correct geometricaberration of the second thin lens, and wherein at least two of theplurality of second scatterers have different height to each other.

A height difference of the at least two second scatterer may be equal toor less than 2λ, with respect to the wavelength λ within thepredetermined wavelength band.

A height H of the plurality of second scatterers may be in a range thatλ/2≤H≤3λ, with respect to the wavelength A within the predeterminedwavelength band.

The second thin lens may further include a low refractive index materiallayer covering the plurality of second scatterers and including amaterial having a refractive index lower than a refractive index ofplurality of the second scatterers; and a plurality of third scattererarranged on the low refractive index material layer and including amaterial having a refractive index higher than a refractive index of thelow refractive index material layer.

The plurality of second scatterers and the plurality of third scatterersmay face each other to be misaligned with each other.

A separation distance in a height direction between adjacent second andthird scatterers among the plurality of second scatterers and theplurality of third scatterers may be greater than λ/2, with respect tothe wavelength λ within the predetermined wavelength band

A shape distribution of the plurality of second scatterers and a shapedistribution of the plurality of third scatterers may be determined tohave different distributions of performance indexes by locations fromeach other.

The shape distribution of the plurality of second scatterers and theshape distribution of the plurality of third scatterers may bedetermined to mutually compensate for non-uniformity in focusingperformance by locations.

At least two of the plurality of third scatterers may have differentheights from each other.

A height difference between at least two of the plurality of thirdscatterers may be equal to or less than 2λ, with respect to thewavelength λ within the predetermined wavelength band.

A height H of a plurality of fourth scatterers may be in a range thatλ/2≤H≤3λ, with respect to the wavelength λ within the predeterminedwavelength band.

At least two of the plurality of first scatterers may have differentheights from each other.

The first thin lens may further include: a low refractive index materiallayer covering the plurality of first scatterers and including amaterial having a refractive index lower than a refractive index of thefirst scatterer; and a plurality of fourth scatterers arranged on thelow refractive index material layer and including a material having arefractive index higher than a refractive index of the low refractiveindex material layer.

The plurality of first scatterers and the plurality of fourth scatterersmay face each other to be misaligned with each other.

A separation distance in a height direction between adjacent first andfourth scatterers among the plurality of first scatterers and theplurality of fourth scatterers may be equal to or less than λ/2, withrespect to the wavelength λ within the predetermined wavelength band.

According to another aspect of the exemplary embodiment, a focusingdevice with respect to light of predetermined wavelength band includes:a substrate; a first thin lens provided at a first surface of thesubstrate and comprising a plurality of first scatterers; and a secondthin lens provided at a second surface of the substrate and comprising aplurality of scatterers, wherein the plurality of first scatterers ofthe first thin lens are configured to correct geometric aberration ofthe second thin lens, and wherein the plurality of scatterers of thesecond thin lens are arranged in multi-layered structure.

The second thin lens may include: a plurality of second scatterersarranged on the second surface; a low refractive index material layercovering the plurality of second scatterers and including a materialhaving a refractive index lower than a refractive index of the pluralityof second scatterers; and a plurality of third scatterers arranged onthe low refractive index material layer and including a material havinga refractive index higher than a refractive index of the low refractiveindex material layer.

The plurality of second scatterers and the plurality of third scatterersmay face each other to be misaligned with each other.

A shape distribution of the plurality of second scatterers and a shapedistribution of the plurality of third scatterers may be determined tomutually compensate for non-uniformity in focusing performance bylocations.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the exemplary embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagram of a focusing device according to a comparativeexample;

FIG. 2 is a diagram of an example in which light is obliquely incidentwith respect to an optical axis of the focusing device of FIG. 1;

FIGS. 3A to 3C are diagrams of light intensity distribution of a focalplane;

FIGS. 4A and 4B are diagrams of light intensity distribution on thefocal plane according to incident angles of light;

FIG. 5 is a focusing device according to an exemplary embodiment;

FIG. 6 is an exemplary diagram of a surface of a second thin lens;

FIGS. 7A to 7C are perspective views of various shapes of first andsecond scatterers;

FIG. 8A is a phase profile of a second thin lens;

FIG. 8B is a diagram of a phase profile of a first thin lens;

FIG. 9 is an exemplary diagram of a path of light incident on thefocusing device of FIG. 5;

FIGS. 10A and 10B are diagrams of light intensity distribution in asubstrate in the focusing device of FIG. 5;

FIGS. 11A to 11F are diagrams of light intensity distribution of animage formed on a focal plane by the focusing device of FIG. 5;

FIG. 12 is a graph of light intensity distribution of an image formed ona focal plane by the focusing device of FIG. 5;

FIG. 13 is an exemplary diagram of forming an image of an object by afocusing device;

FIG. 14 is a graph of a relationship between locations of focusingpoints and incident angles of light;

FIG. 15 is an exemplary diagram of an arrangement of first and secondscatterers;

FIGS. 16A to 16C are diagrams for describing changes in paths ofincident light according to wavelengths of the incident light;

FIGS. 17A to 17C are diagrams of light intensity distribution of animage formed on a focal plane by light incident in parallel to anoptical axis of a focusing device;

FIG. 18 is a diagram of changes in light intensity distribution of animage according to wavelengths and incident angles of incident light;

FIG. 19 is a diagram of a focusing device according to another exemplaryembodiment;

FIG. 20 is an imaging device according to another exemplary embodiment;

FIG. 21 is a diagram of a beam scanner according to an exemplaryembodiment;

FIG. 22 is a diagram of a scope device according to another exemplaryembodiment; and

FIG. 23 is an exemplary diagram of observing a target object by using ascope device.

FIG. 24 is a diagram of a focusing device according to another exemplaryembodiment.

FIG. 25 is an exemplary diagram of classification of regions related tothe arrangement of second scatterers provided in a second thin lens ofthe focusing device of FIG. 24.

FIG. 26 is a graph conceptually showing a target phase for eachwavelength to be satisfied by scatterers in each region of FIG. 25.

FIG. 27 is a diagram of a focusing device according to another exemplaryembodiment.

FIG. 28 is an exemplary diagram of the second scatterers arranged in oneregion of a first layer of the second thin lens in the focusing deviceof FIG. 27.

FIG. 29 is an exemplary diagram of design data of a pitch and a width bylocations of the second scatterers arranged in the first layer of thesecond thin lens of the focusing device of FIG. 27.

FIG. 30 is a graph of a comparison between a target phase value and aphase value by the scatterers designed as in FIG. 28.

FIG. 31 is a graph of a performance index obtained by quantifying adifference between a target value and a design value in FIG. 30.

FIG. 32 is a diagram of a focusing device according to another exemplaryembodiment.

FIG. 33 is a diagram of a focusing device according to another exemplaryembodiment.

FIG. 34 is a diagram of a focusing device according to another exemplaryembodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout. In this regard,the present exemplary embodiments may have different forms and shouldnot be construed as being limited to the descriptions set forth herein.Accordingly, the exemplary embodiments are merely described below, byreferring to the figures, to explain aspects. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings.

The terms used in the exemplary embodiments are selected as generalterms used currently as widely as possible considering the functions inthe present disclosure, but they may depend on the intentions of one ofordinary skill in the art, practice, the appearance of new technologies,etc. In specific cases, terms arbitrarily selected by the applicant arealso used, and in such cases, their meaning will be described in detail.Thus, it should be noted that the terms used in the specification shouldbe understood not based on their literal names but by their givendefinitions and descriptions through the specification.

Throughout the specification, it will also be understood that when anelement is referred to as being “connected to” another element, it canbe directly connected to the other element, or electrically connected tothe other element while intervening elements may also be present. Also,when a part “includes” or “comprises” an element, unless there is aparticular description contrary thereto, the part can further includeother elements, not excluding the other elements. In addition, the termssuch as “unit,” “-er (-or),” and “module” described in the specificationrefer to an element for performing at least one function or operation,and may be implemented in hardware, software, or the combination ofhardware and software.

The terms “configured of” or “includes” should not be construed asnecessarily including all elements or operations described in thespecification. It will be understood that some elements and someoperations may not be included, or additional elements or operations maybe further included.

While such terms as “first,” “second,” “A,” “B,” etc., may be used todescribe various components, such components must not be limited to theabove terms. The above terms are used only to distinguish one componentfrom another.

The present exemplary embodiments may have different forms and shouldnot be construed as being limited to the descriptions set forth herein.Elements and features that may be easily derived by one of ordinaryskill in the art to which the present disclosure pertains are within thespirit and scope of the present disclosure as defined by the appendedclaims. Hereinafter, the present exemplary embodiments will be describedwith reference to the accompanying drawings.

FIG. 1 is a diagram of a focusing device according to a comparativeexample.

Referring to FIG. 1, the focusing device according to the comparativeexample may include a substrate 10 and a plurality of scatterers 20provided at a side of the substrate 10. In the focusing device of FIG.1, a path of light exiting the substrate 10 may change as light passesthrough the plurality of scatterers 20. Shapes and materials of theplurality of scatterers 20 may vary according to functions performed bythe plurality of scatterers 20. For example, the plurality of scatterers20 of the focusing device of FIG. 1 may have a shape and a sizeappropriate for performing a function of a lens with positive refractivepower. Also, as shown in FIG. 1, the plurality of scatterers 20 mayallow light that is perpendicularly incident on the substrate 10 to forma focusing point at a focal plane S0.

FIG. 2 is a diagram of an example in which light is obliquely incidentwith respect to an optical axis (z-axis) of the focusing device of FIG.1;

Referring to FIG. 2, light incident in a direction that is not parallelto the optical axis of the focusing device may pass through theplurality of scatterers 20 but not focus on a single focusing point.Such phenomenon is referred to as geometric aberration. The geometricaberration may include coma aberration and field of curvatureaberration. The aforementioned geometric aberration may decreasesharpness of images formed by the focusing device. Also, the geometricaberration limits a field of view (FOV) of the focusing device.

FIGS. 3A to 3C are diagrams of light intensity distribution of a focalplane.

FIG. 3A shows light intensity distribution of an image formed by lightthat is parallel to the optical axis (z-axis) of the focusing device.FIG. 3B shows light intensity distribution of an image formed by lightincident at an incident angle of 1° with respect to the optical axis.FIG. 3C shows light intensity distribution of an image formed by lightincident at an incident angle of 3° with respect to the optical axis.Bars at a right hand side of FIGS. 3A to 3B indicates relative intensityof light.

Referring to FIG. 3A, when an incident angle of light is 0° (i.e., whenlight is parallel to the optical axis of the focusing device), an areawith high light intensity distribution may be narrow. That is, afocusing effect of the focusing device may be relatively excellent.Referring to FIG. 3B, when the incident angle of light is 1°, an areawith high intensity of light is wide. As the incident angle of lightincreases, the focusing effect of the focusing device may decrease.Referring to FIG. 3C, when the incident angle of light is 3°, intensityof light may decrease in a central area of the image. However,peripheral areas of the image may have greater intensity of light as theincident angle increases. That is, even when the incident angle of lightincreases by a small amount, the focusing effect of the focusing devicemay substantially decrease.

FIGS. 4A and 4B are diagrams of light intensity distribution on thefocal plane S0 according to incident angles of light.

Referring to FIG. 4A, as the incident angle of light increases, peaksmay be differently located in a graph of light intensity distribution.Also, as the incident angle increases, the graph of light intensitydistribution may be widened and peak values may decrease. Referring toFIG. 4B, when the incident angle is 3° or higher, peak values of thelight intensity distribution may decrease below more than half of peakvalues of when the incident angle is 0°. Also, a range of lightintensity distribution may substantially increase. When the incidentangle of light exceeds about 1°, image distortion due to coma aberrationmay increase.

FIG. 5 is a focusing device 100 according to an exemplary embodiment.

Referring to FIG. 5, the focusing device 100 according to an exemplaryembodiment may include a substrate 110, a first thin lens 120 includinga plurality of first scatterers 122 provided on a first surface S1 ofthe substrate 110, and a second thin lens 130 including a plurality ofsecond scatterers 132 provided on a second surface S2 of the substrate110.

The substrate 110 may be shaped as a plate. The first and secondsurfaces S1 and S2 of the substrate 110 may be substantially parallel toeach other. However, the first and second surfaces S1 and S2 do not haveto be completely parallel to each other but may be oblique with respectto each other. The substrate 110 may include a transparent material. Thetransparent material indicates a material with a high light transmissionrate. For example, the substrate 110 may include at least one selectedfrom glass (fused silica, BK7, etc.), quartz, polymer (PMMA, SU-8,etc.), and plastic.

The first thin lens 120 may include the plurality of first scatterers122 that are arranged on the first surface S1 of the substrate 110.Also, the second thin lens 130 may include the plurality of secondscatterers 132 that are arranged on the second surface S2 of thesubstrate 110. Unlike optical lenses of the related art, the first andsecond thin lenses 120 and 130 may change a path of light by using theplurality of first and the plurality of second scatterers 122 and 132.The plurality of first and the plurality of second scatterers 122 and132 may capture light incident near one another and resonate lightinside the plurality of first and the plurality of second scatterers 122and 132. The plurality of first and the plurality of second scatterers122 and 132 may adjust transmission and reflection properties of thelight incident on the plurality of first and the plurality of secondscatterers 122 and 132. For example, the plurality of first and theplurality of second scatterers 122 and 132 may modulate at least one ofan amplitude, phase, and polarization of transmitted light according tostructures and included materials of the plurality of first and theplurality of second scatterers 122 and 132. The plurality of first andthe plurality of second scatterers 122 and 132 may be arranged such thatdistribution of at least one of an amplitude, phase, and polarization ofthe transmitted light is modulated and thus a wavefront of thetransmitted light changes with respect to a wavefront of the incidentlight. Therefore, the plurality of first and the plurality of secondscatterers 122 and 132 may change a proceeding direction of thetransmitted light with respect to that of the incident light.

The second thin lens 130 may function as a lens with positive refractivepower. Shapes, sizes, materials, and an arrangement pattern of theplurality of second scatterers 132 may be modified so that the secondthin lens 130 has positive refractive power. Also, the plurality ofsecond scatterers 132 may be designed such that the second thin lens 130does not cause spherical aberration. To do so, the shapes, the sizes,the materials, and the arrangement of the plurality of second scatterers132 may vary according to a location on a surface of the substrate 110where the plurality of second scatterers 132 are arranged.

FIG. 6 is an exemplary diagram of a surface of the second thin lens 130.

Referring to FIG. 6, the plurality of second scatterers 132 may bearranged on the surface of the second thin lens 130. Waveform of lightthat passed through the second thin lens 130 may vary according toshapes, arrangement intervals, and an arrangement pattern of theplurality of second scatterers 132. When the plurality of secondscatterers 132 are arranged on the surface of the second thin lens 130as shown in FIG. 6, the second thin lens 130 may function as a lens withpositive refractive power.

The plurality of first scatterers 122 of the first thin lens 120 may bedesigned to correct coma aberration of the second thin lens 130. Shapes,materials, and arrangement pattern of the plurality of first scatterers122 may vary depending on a thickness of the substrate 110 and theshapes, the materials, and the arrangement pattern of the plurality ofsecond scatterers 132. In a general optical system, a plurality ofoptical lenses are combined to correct coma aberration of lenses.Therefore, the general optical system may be difficult to design andsize reduction may be difficult. However, the focusing device 100according to an exemplary embodiment may have the first and second thinlenses 120 and 130 on both surfaces of the substrate 110 by arrangingthe plurality of first and plurality of second scatterers 122 and 132 onthe both surfaces of the substrate 110. Accordingly, size reduction ofthe focusing device 100 may become convenient. Also, since the firstthin lens 120 may correct coma aberration of the second thin lens 130,the focusing device 100 may have a wide FOV.

FIGS. 7A to 7C are perspective views of various shapes of the individualscatterers of plurality of first and plurality of second scatterers 122and 132.

Referring to FIGS. 7A to 7C, the individual scatterers of the pluralityof first and the individual scatterers of the plurality of secondscatterers 122 and 132 in the first and second thin lenses 120 and 130may have a pillar structure. Such pillar structure may have any one ofcircular, oval, rectangular, and square cross-sections. FIG. 7A shows ascatterer shaped as a pillar with a circular cross-section. FIG. 7Bshows a scatterer shaped as a pillar with an oval cross-section. FIG. 7Cshows a scatterer shaped as a pillar with a quadrilateral cross-section.The pillar structure may be inclined at an angle in a height direction.

Although exemplary shapes of the plurality of first and the plurality ofsecond scatterers 122 and 132 are shown in FIGS. 7A to 7C, exemplaryembodiments are not limited thereto. For example, the plurality of firstand plurality of second scatterers 122 and 132 may be shaped aspolyhedral pillars or pillars with an L-shaped cross-section. The shapesof the plurality of first and plurality of second scatterers 122 and 132may be asymmetrical in a direction. For example, respectivecross-sections of the plurality of first and the plurality of secondscatterers 122 and 132 may be asymmetrical in a horizontal direction.Also, since the respective cross-sections of the plurality of first andthe plurality of second scatterers 122 and 132 may vary according torespective heights of the plurality of first and the plurality of secondscatterers 122 and 132, respective shapes of the plurality of first andthe plurality of second scatterers 122 and 132 may be asymmetrical withrespect to the respective heights thereof.

Respective refractive indexes of the plurality of first and theplurality of second scatterers 122 and 132 may be higher than arefractive index of the substrate 110. For example, the respectiverefractive indexes of the plurality of first and the plurality of secondscatterers 122 and 132 may be greater than the refractive index of thesubstrate 110 by approximately 1 or more. Therefore, the substrate 110may include a material with a relatively low refractive index, and theplurality of first and the plurality of second scatterers 122 and 132may include a material with a relatively high refractive index. Forexample, the plurality of first and the plurality of second scatterers122 and 132 may include at least one selected from crystalline silicon(c-Si), polycrystalline silicon (poly Si), amorphous silicon, Si₃N₄,GaP, GaAs, TiO₂, AlSb, AIAs, AlGaAs, AlGaInP, BP, and ZnGeP₂. Theplurality of first and the plurality of second scatterers 122 and 132may be additionally surrounded by materials with a low refractive index(SiO₂, polymer (PMMA, SU-8, etc.)) in upper and horizontal directions.

FIG. 8A is a phase profile of the second thin lens 130.

Referring to FIG. 8A, a phase shift of light incident on the second thinlens 130 may decrease from a central area of the second thin lens 130 toa peripheral area of the second thin lens 130. When the second thin lens130 is configured such that the phase profile shown in FIG. 8A issatisfied, the second thin lens 130 may function as a lens with positiverefractive power. Also, spherical aberration that occurs in generaloptical lenses may be decreased. The phase profile of the second thinlens 130 shown in FIG. 8A is merely exemplary, and exemplary embodimentsare not limited thereto. For example, a shape of the phase profile maybe changed according to a diameter, a focal length, etc. of the secondthin lens 130 changes.

Design conditions of the plurality of second scatterers 132 in thesecond thin lens 130 may be modified according to the phase profile ofthe second thin lens 130. For example, at least one of the shapes, thesizes, the materials, and the arrangement pattern of the plurality ofsecond scatterers 132 may be modified according to an arranged locationof the plurality of second scatterers 132 on the surface of thesubstrate 110. The shapes, the sizes, the materials, and the arrangementpattern of the plurality of second scatterers 132 may be determinedaccording to an amount of unwrapped phase shift of light that passesthrough the plurality of second scatterers 132. The amount of unwrappedphase shift indicates a phase component corresponding to a phase shiftvalue between 0 and 2π remaining after subtracting an integer multipleof 2π from an amount of phase shift. Respective structures and materialsof the plurality of first and the plurality of second scatterers 122 and132 may vary according to the amount of unwrapped phase shift of lightthat passes through the plurality of first and the plurality of secondscatterers 122 and 132.

FIG. 8B is a diagram of a phase profile of the first thin lens 120.

Referring to FIG. 8B, a phase shift of light incident on the first thinlens 120 may decrease from a peripheral area of the first thin lens 120to a middle area of the first thin lens 120 and then increase again fromthe middle area of the first thin lens 120 to a central area of thefirst thin lens 120. For example, as shown in FIG. 8B, the first thinlens 120 may have a phase profile in which the phase shift of theincident light decreases from the central area to a middle area having adiameter of approximately 150 μm and increases from the middle area tothe peripheral area. When the first thin lens 120 is configured suchthat the phase profile shown in FIG. 8B is satisfied, the first thinlens 120 may change a path of the incident light and thus correct comaaberration of the second thin lens 130. The phase profile of the firstthin lens 120 shown in FIG. 8B is merely exemplary, and exemplaryembodiments are not limited thereto. For example, a specific shape ofthe phase profile of the first thin lens 120 may be changed according toa diameter, a focal length, etc. of the first thin lens 120. Also, thespecific shape of the phase profile of the first thin lens 120 may bechanged according to the phase profile of the second thin lens 130 andthe thickness of the substrate 110.

FIG. 9 is an exemplary diagram of a path of light incident on thefocusing device 100 of FIG. 5.

Referring to FIG. 9, light may be incident on the focusing device 100 ina direction that is not parallel to the optical axis (z-axis) of thefocusing device 100. A path of light incident on the first thin lens 120may be changed by the plurality of first scatterers 122. After the pathis changed by the plurality of first scatterers 122, the light may passthrough the substrate 110, and the path of the light may be changedagain by the plurality of second scatterers 132. The first and secondthin lenses 120 and 130 may correct coma aberration of one another.Also, the first and second thin lenses 120 and 130 may allow the lightto form a focusing point on the focal plane S0 regardless of angles atwhich light is incident on the first surface S1 of the substrate 110.

FIGS. 10A and 10B are diagrams of light intensity distribution insidethe substrate 110 in the focusing device 100 of FIG. 5.

FIG. 10A shows an example in which light is incident in a directionparallel to an optical axis of the focusing device 100, and FIG. 10Bshows an example in which light is obliquely incident (at an incidentangle of 12°) with respect to the optical axis of the focusing device100. Referring to FIGS. 10A and 10B, light intensity distribution in thesubstrate 110 may vary according to an incident angle of light becausethe plurality of first scatterers 122 change a path of light thatproceeds into the substrate 110. Also, coma aberration of the focusingdevice 100 may be corrected by changing the light intensity distributionin the substrate 110.

FIGS. 11A to 11F are diagrams of light intensity distribution of animage formed on the focal plane S0 by the focusing device 100 of FIG. 5.

FIG. 11A shows light intensity distribution of an image formed by lightincident in parallel to an optical axis of the focusing device 100. FIG.11B shows light intensity distribution of an image formed by lightincident at an incident angle of 3°. FIG. 11C shows light intensitydistribution of an image formed by light incident at an incident angleof 6°. FIG. 11D shows light intensity distribution of an image formed bylight incident at an incident angle of 9°. FIG. 11E shows lightintensity distribution of an image formed by light incident at anincident angle of 12°. FIG. 11F shows light intensity distribution of animage formed by light incident at an incident angle of 15°. Bars at aright hand side of FIGS. 11A to 11F indicates intensity of light.

Referring to FIGS. 11A to 11F, a location of a focusing point may changeas an incident angle of light changes from 0° to 15°. However, a shapeof light intensity distribution may nearly not change at the location ofthe focusing point. By using the focusing device 100 of FIG. 5,intensity of light at the focusing point may be almost maintained at asteady rate even when the incident angle of light changes. Also, unlikeFIGS. 3A to 3C, the focusing device 100 of FIG. 5 may prevent defocusingeven when the incident angle of light increases.

FIG. 12 is a graph of light intensity distribution of an image formed onthe focal plane S0 by the focusing device 100 of FIG. 5.

Referring to FIG. 12, a location of a focusing point may change as anincident angle changes from 0° to 15°. However, a shape and a peak oflight intensity distribution graph may almost not change at the locationof the focusing point. Also, unlike FIGS. 4A and 4B, the graph may showonly one peak instead of a plurality of peaks even when the incidentangle of light increases. As shown in FIG. 12, coma aberration of thefocusing device 100 may be corrected. Therefore, even when the incidentangle of light changes, the shape of the light intensity distributionmay almost not change at the focusing point. Also, the focusing device100 may have a wide FOV.

FIG. 13 is an exemplary diagram of forming an image of an object by thefocusing device 100.

For convenience, the focusing device 100 and an image are enlarged inFIG. 13 and are not drawn to scale. However, an actual distance betweenan object and the focusing device 100 and a size of the object may besubstantially different from a height of the focusing device 100.Therefore, when light reflected from a point of the object is incidenton the focusing device 100, the light may be substantially parallelrays. Referring to FIG. 13, a distance h between a location of afocusing point and an optical axis of the focusing device 100 may varyaccording to an angle θ at which light is incident. For example, whenthe focusing device 100 is designed such that image distortion is notcreated, the distance h between the location of the focusing point andthe optical axis of the focusing device 100 may satisfy Equation 1.h=f*tan θ  [Equation 1]

In Equation 1, ‘h’ is the distance between the location of the focusingpoint and the optical axis of the focusing device 100, T is an effectivefocal length of the focusing device 100, and ‘θ’ is an incident angle oflight.

As another example, when the focusing device 100 is provided as anorthographic fisheye lens to enlarge the FOV of the focusing device 100,the distance h between the location of the focusing point and theoptical axis of the focusing device 100 may satisfy Equation 2h=f*sin θ  [Equation 2]

In Equation 2, ‘h’ is the distance h between the location of thefocusing point and the optical axis of the focusing device 100, ‘f’ isan effective focal length of the focusing device 100, and ‘θ’ is anincident angle of light.

FIG. 14 is a graph of a relationship between locations of focusingpoints and incident angles of light.

In FIG. 14, a solid line indicates the focusing device 100 forming adistortion free image, and a dashed line indicates the focusing device100 provided as an orthographic fisheye lens. A location at which animage is formed according to incident angles of light may be changed bymodifying designs of the plurality of first and the plurality of secondscatterers 122 and 132. Accordingly, an image distortion degree and theFOV of the focusing device 100 may be adjusted. For example, when imageaccuracy is required, an image formed by light that passed through thefocusing device 100 may be determined according to the solid line ofFIG. 14. As another example, a wide FOV is required, an image formed bylight that passed through the focusing device 100 may be determinedaccording to the dashed line of FIG. 14.

The focusing device 100 of FIG. 5 may focus incident light according towavelengths of incident light.

The first and second thin lenses 120 and 130 may differently change adirection of incident light according to wavelengths of the incidentlight. Therefore, the focusing device 100 according to an exemplaryembodiment may only allow incident light within a certain wavelengthband to form a focusing point on the focal plane S0. Also, the first andsecond thin lenses 120 and 130 may differently correct coma aberrationaccording to the wavelengths of the incident light. A wavelength oflight that is allowed by the focusing device 100 to form the focusingpoint on the focal plane S0 is a design wavelength of the focusingdevice 100. Design conditions of the plurality of first and theplurality of second scatterers 122 and 132 may vary according to thewavelength of light that is to be focused by the focusing device 100,i.e., the design wavelength of the focusing device 100.

FIG. 15 is an exemplary diagram of an arrangement of the plurality offirst and the plurality of second scatterers 122 and 132.

Referring to FIG. 15, intervals T between the plurality of first and theplurality of second scatterers 122 and 132, respective heights h of theplurality of first and the plurality of second scatterers 122 and 132,and an arrangement pattern of the plurality of first and the pluralityof second scatterers 122 and 132 may be determined according to thedesign wavelength of the focusing device 100. The intervals T betweenthe plurality of first and the plurality of second scatterers 122 and132 may be less than the design wavelength. For example, the intervalsbetween the plurality of first and the plurality of second scatterers122 and 132 may be equal to or less than ¾ or ⅔ of the designwavelength. Also, the respective heights h of the plurality of first andthe plurality of second scatterers 122 and 132 may be less than thedesign wavelength. For example, the respective heights h of theplurality of first and the plurality of second scatterers 122 and 132may be equal to or less than ⅔ of the design wavelength.

FIGS. 16A to 16C are diagrams for describing changes in path of incidentlight according to wavelengths of the incident light. The focusingdevice 100 of FIGS. 16A to 16C are designed to be appropriate forfocusing about light having a wavelength of 850 nm.

Referring to FIG. 16A, when light having a wavelength that correspondsto the design wavelength of the focusing device 100 is incident, afocusing point of the light may be formed on the focal plane S0regardless of an incident angle of the light. However, referring to FIG.16B, when light having a wavelength (830 nm) that is less than thedesign wavelength is incident, the light may reach the focal plane S0before a focusing point of the light is formed. Also, referring to FIG.16C, when light having a wavelength (870 nm) that is greater than thedesign wavelength is incident, a focusing point may be formed before thelight reaches the focal plane S0.

FIGS. 17A to 17C are diagrams of light intensity distribution of animage formed on the focal plane S0 by light incident in parallel to anoptical axis of the focusing device 100.

Referring to FIG. 17B, an image formed by light having a wavelength (850nm) corresponding to the design wavelength of the focusing device 100may have narrow light intensity distribution. However, referring toFIGS. 17A and 17C, an image formed by light having a wavelength (830 nmor 870 nm) different from the design wavelength of the focusing device100 may have wide light intensity distribution. That is, when thewavelength of incident light is different from the design wavelength ofthe focusing device 100, a focusing effect of the light incident inparallel to the optical axis of the focusing device 100 may decrease.

FIG. 18 is a diagram of changes in light intensity distribution of animage according to wavelengths and incident angles of incident light.

Referring to FIG. 18, when a wavelength of incident light corresponds toa design wavelength (850 nm), a focusing effect may not decrease untilan incident angle reaches 20°. Also, when the incident angle is equal to40°, light intensity distribution may change by a minor degree. However,when light has a wavelength of 810 nm, there may be a significant changein light intensity distribution as an incident angle changes to 20°.Also, when light has a wavelength of 870 nm, there may be a significantchange in light intensity distribution as an incident angle changes to40°. That is, when the wavelength of incident light is different fromthe design wavelength of the focusing device 100, the focusing device100 may be less effective in correcting coma aberration.

FIG. 19 is a diagram of a focusing device 100 according to anotherexemplary embodiment.

Referring to FIG. 19, the focusing device 100 may include an opticalfilter 160 that blocks wavelengths of the incident light which aredifferent from the design wavelength of the focusing device 100. Theoptical filter 160 may transmit light having a wavelength equal orsimilar to the design wavelength of the focusing device 100 from theincident light. Also, the optical filter 160 may reflect or absorb lighthaving a wavelength that is not similar to the design wavelength. Theoptical filter 160 may filter the wavelength of incident light and thusprevent a light component with a weak focusing effect from reaching afocal plane S0.

FIG. 20 is an imaging device according to another exemplary embodiment.

Referring to FIG. 20, the imaging device may include the focusing device100 of FIG. 5, and an optical detector 140 that detects light thatpassed through the focusing device 100. The optical detector 140 mayinclude an optical detection layer 144 provided at the focal plane S0 ofthe focusing device 100 and a cover glass 142 that protects the opticaldetection layer 144 and the optical detection layer 144. The opticaldetection layer 144 may include a plurality of charge-coupled devices(CCDs), complementary metal-oxide semiconductor (CMOS) sensors, photodiodes, etc. The optical detection layer 144 may convert optical signalsincident on the optical detection layer 144 into electric signals.

FIG. 21 is a diagram of a beam scanner 200 according to an exemplaryembodiment.

Referring to FIG. 21, the beam scanner 200 may include the focusingdevice 100 of FIG. 5. Also, the beam scanner 200 may include a lightsource array 220 that includes a plurality of light sources 222. Thelight source array 220 may be provided at a location of the focal planeS0 of the focusing device 100 of FIG. 5. Therefore, a distance betweenthe light source array 220 and the focusing device 100 may varyaccording to an effective focal length of the focusing device 100.

The focusing device 100 may focus incident light to another locationaccording to an incident angle of the light incident on the firstsurface S1 of the substrate 110. Similarly, a path of light that passedthrough the focusing device 100 may change depending on respectivelocations of the plurality of light sources 222 emitting light from thelight source array 220 facing the second surface S2 of the substrate110. For example, as shown in FIG. 21, paths of light rays L1 and lightrays L2 that passed through the focusing device 100 may change accordingto the respective locations of the plurality of light sources 222emitting light. Also, the light rays L1 and L2 that passed through thefocusing device 100 may be parallel rays. Therefore, the focusing device100 may function as an optical path modifier of the beam scanner 200.

Since the first and second thin lenses 120 and 130 are designed tocorrect coma aberration of each other, the focusing device 100 may havea wide FOV. Accordingly, an area of the light source array 220 may beless limited. Also, the light source array 220 may adjust the respectivelocations of the plurality of light sources 222 and thus easily adjustdirection of light emitted by the beam scanner 200.

FIG. 22 is a diagram of a scope device 300 according to anotherexemplary embodiment. Referring to FIG. 22, the scope device 300 mayinclude a focusing device 100, and a light source 310 arranged to face asecond surface S2 of a substrate 110 of the focusing device 100 andemitting light on a target object 10. Light emitted from the lightsource 310 may pass through the target object 10 and be incident on thefocusing device 100. Also, since the focusing device 100 may function asa focusing lens, the focusing device 100 may be used as an object lensof the scope device 300. In this case, the scope device 300 refers to adevice for observing objects that are small or far away, such as amicroscope or a telescope. Since the focusing device 100 has a wide FOV,the scope device 300 may observe a large area of the target object 10without coma aberration.

FIG. 23 is an exemplary diagram of 3-dimensional (3D) volumetric imaginga target object 20 by using the scope device 300.

Referring to FIG. 23, when the light source 310 emits light havingvarious wavelengths on the target object 20, the focusing device 100 ofthe scope device 300 may function as an object lens that has differentfocal lengths with respect to the target object 20 according to thewavelengths of the light emitted from the light source 310. The lightsource 310 may emit light having different wavelengths on the targetobject 20 according to time variation. Alternatively, the light source310 may simultaneously emit light having different wavelengths on thetarget object 20. The scope device 300 may divide light that passedthrough the target object 20 according to its wavelengths and recordimages of the target object 20. Also, the scope device 300 may analyzethe images according to the wavelengths of light, and thus extract a 3Dimage including depth information of the target object 20.

Examples of focusing devices according to various embodiments aredescribed below. The below-described focusing devices may be applied tovarious optical devices, for example, the above-described imagingdevices, scope devices, or beam scanners.

FIG. 24 is a diagram of a focusing device 1000 according to anotherexemplary embodiment. FIG. 25 is an exemplary diagram of classificationof regions related to the arrangement of second scatterers provided in asecond thin lens 1300 of the focusing device 1000 of FIG. 24. FIG. 26 isa graph conceptually showing a target phase for each wavelength to besatisfied by the scatterers in each region of FIG. 25.

Referring to FIG. 24, the focusing device 1000 for focusing light of apredetermined wavelength band on a predetermined focal plane S0 mayinclude the substrate 110, a first thin lens 1200 including a pluralityof first scatterers NS1 formed on a first surface S1 of the substrate110, and the second thin lens 1300 including a plurality of secondscatterers NS2 formed on a second surface S2 of the substrate 110.

Like the above-described embodiments, the first scatterers NS1 of thefirst thin lens 1200 may be configured to correct geometric aberrationof the second thin lens 1300, and the second scatterers NS2 may beconfigured so that the second thin lens 1300 may function as a lens withpositive refractive power.

Furthermore, a low refractive index material layer 190 including amaterial with a refractive index lower than that of the first scatterersNS1 and covering the first scatterers NS1 may be further provided toprotect the first scatterers NS1, and a low refractive index materiallayer 180 including a material with a refractive index lower than thatof the second scatterers NS2 and covering the second scatterers NS2 maybe further provided to protect the second scatterers NS2. The lowrefractive index material layers 180 or 190 may be omitted.

In the present embodiment, at least two of the second scatterers NS2provided in the second thin lens 1300 may have different heights H fromeach other. A height difference ΔH between at least two secondscatterers NS2 may be equal to or less than 2λ with respect to awavelength λ within the predetermined wavelength band. The respectiveheights H of the second scatterers NS2 may be in a range that λ/2≤H≤3λwith respect to the wavelength λ within the predetermined wavelengthband.

The second scatterers NS2 have different heights from each other tofurther freely adjust chromatic aberration, that is, dispersionaccording to wavelengths, when focusing light of a relatively widewavelength band on the focal plane S0.

In order to have refractive power to incident light, the classificationof regions of FIG. 25 may be used for determining the shapes of thesecond scatterers NS2 and arranging the second scatterers NS2. Apredetermined rule regarding the sizes and arrangement of the secondscatterers NS2 is applied to each of a plurality of regions R₁, R₂, . .. R_(k), . . . R_(N). A target phase φ_(target) as illustrated in FIG.26 may be set to each region. The target phase φ_(target) may be set toindicate a phase change range of 2π with respect to a central wavelengthλ_(m) in the region given in FIG. 25, and thus the regions R₁, R₂, . . .R_(k), . . . R_(N) may be referred to as the “2π zone”. In the verticalaxis of the graph of FIG. 26, the negative (−) sign is shown as anexample of being a phase for indicating positive refractive power.

The target phase φ_(target) target may slightly vary according to lightof different wavelengths λ_(l), λ_(m), and λ_(s), as illustrated in FIG.26. In order to implement a desired target phase to each light of adetermined wavelength, a rule regarding the shape, size, and arrangementof the second scatterers NS2 arranged in a plurality of 2π zones may bedetermined. In the following description, an expression “shapedistribution” may be used together as an expression meaning the “shape,size, and arrangement”. A degree that the target phase φ_(target) variesaccording to light of a different wavelength is related to a dispersionΔφ, and a wavelength range including presented examples λ_(l), λ_(m),and λ_(s) is related to a bandwidth BW. A shape condition of each of thesecond scatterers NS2 which may implement a dispersion Δφ within adesired range with respect to desired bandwidth BW may be set from aphase-dispersion map prepared in advance. A phase-dispersion map may begenerally created by a method of setting the second scatterers NS2 to acertain height and marking a shape condition at a position correspondingto (phase, dispersion) at the central wavelength by various combinationsof a width and a pitch. A design dimension that may produce desiredperformance at a desired position may be selected from the map. When aheight variation is introduced, a plurality of phase-dispersion mapshaving different height conditions from each other may be set to overlapeach other, that is, a range of selecting the shape of the secondscatterers NS2 may extend. As such, the shape and arrangement of thesecond scatterers NS2 may be determined so as to freely correctchromatic aberration while increasing a focusing wavelength band.

Although FIG. 24 randomly illustrates the height H, width w, and pitch pof each of the second scatterers NS2, this is merely for convenience ofexplanation, and the present disclosure is not limited thereto. Forexample, a predetermined rule may be set and applied not only to thewidth and pitch but also to the height in the region as illustrated inFIG. 25.

FIG. 27 is a diagram of a focusing device 1001 according to anotherexemplary embodiment.

Referring to FIG. 27, the focusing device 1001 may include the substrate110, the first thin lens 1200 including the first scatterers NS1 formedon the first surface S1 of the substrate 110, and a second thin lens1301 including a plurality of scatterers formed on the second surface S2of the substrate 110.

As in the above-described embodiments, the first thin lens 1200 may beconfigured to correct geometric aberration of the second thin lens 1301,and the second thin lens 1301 may be configured to function as a lenswith positive refractive power.

In the present embodiment, the second thin lens 1301 may have ascatterer arrangement of a plurality of layers. The second thin lens1301 may include the second scatterers NS2 formed on the second surfaceS2 of the substrate 110, the low refractive index material layer 180covering the second scatterers NS2 and including a material having arefractive index lower than the refractive index of the secondscatterers NS2, and a plurality of third scatterers NS3 formed on thelow refractive index material layer 180 and including a material havinga refractive index higher than the refractive index of the lowrefractive index material layer 180. The second scatterers NS2 form afirst layer LA1, and the third scatterers NS3 form a second layer LA2. Alow refractive index material layer 185 that covers the third scatterersNS3 and including a material having a refractive index lower than therefractive index of the third scatterers NS3 may be further provided.The low refractive index material layer 185 may protect the thirdscatterers NS3 and may planarize an upper surface of the second thinlens 1301. The low refractive index material layer 185 may be omitted.

The second scatterers NS2 and the third scatterers NS3 may face eachother to be misaligned with each other. This means that the center axesof at least some of the second scatterers NS2 and the third scatterersNS3 vertically facing each other may be misaligned with each other.Also, it is not limited to that all of the second scatterers NS2 and thethird scatterers NS3 face each other to be misaligned with each other.

An interval d between the second scatterer NS2 and the third scattererNS3, which are adjacent to each other, among the second scatterers NS2and the third scatterers NS3, that is, a separation distance in a heightdirection (Z direction), may be greater than λ/2 with respect to thewavelength λ within the predetermined wavelength band.

The arrangement of the second and third scatterers NS2 and NS3 in amultilayer is to reduce deterioration of performance that may occur atsome positions even when the shape of each scatter is set to a desiredtarget phase. In this regard, a description is presented with referenceto FIGS. 25, 26, and 28 to 31.

The classification of regions in FIG. 25 and the target phases of therespective regions in FIG. 26 may be applied to the second thin lens1301 of FIG. 27. In other words, the sizes and arrangements of thesecond scatterers NS2 and the third scatterers NS3 arranged in the firstlayer LA1 and the second layer LA2 of the second thin lens 1301 may beset to satisfy the target phase of FIG. 26 for each region. FIG. 28 isan exemplary diagram of the second scatterers NS2 arranged in one regionof the first layer LA1 of the second thin lens 1301 of FIG. 27. Thearrangement rule of the width w and the pitch p may be repeated in aplurality of regions. FIG. 29 is an exemplary diagram of design data ofthe width w and the pitch p by locations of the second scatterers NS2arranged in the first layer LA1 of the second thin lens 1301 of thefocusing device 1001 of FIG. 27.

FIG. 30 is a graph of a comparison between a target phase value and aphase value by the scatterers designed as in FIG. 28. In the graph, atarget phase value graph is indicated by “target”, and a phase valuegraph by the scatterers designed to implement the target phase isindicated by “designed”. In the graph, the two graphs are not completelycongruous with each other and have an error. Furthermore, a degree ofmismatch appears to vary according to the position.

FIG. 31 is a graph of a performance index obtained by quantifying adifference between a target value and a design value in FIG. 30. Theperformance index is obtained such that correlation degree between atarget transmissivity (transmission intensity and transmission phase)and an actual transmissivity in an entire wavelength band to beconsidered is integrated and quantified by locations in a radialdirection. The graph may be referred to as the “merit function”. Thecorrelation degree is good as a value on the vertical axis of the graphis close to 1, and a position where the correlation degree is the lowestmay be known from points Q indicating the lower extreme points.

FIGS. 29 to 31 illustrate the design data of the first layer LA1, and asmultiple layers are introduced, correlation properties that arenon-uniformly low may be compensated. For example, the rule regardingthe size and arrangement of the third scatterers NS3 forming the secondlayer LA2 may be determined such that, as illustrated in FIG. 31, aposition where correlation is low in the first layer LA1, for example,the extreme point Q, may be moved to another position. By making theposition where correlation is low appear to be different in the firstlayer LA1 and the second layer LA2 and overlapping dispersion and phasefeatures of each layer, when desired light of a predetermined wavelengthband is to be focused while maintaining dispersion in an appropriaterange, performance deterioration that may occur at some particularpositions may be reduced.

The shape distribution of the second scatterers NS2 provided in thefirst layer LA1 and the shape distribution of the third scatterers NS3provided in the second layer LA2 may be determined to have differentdistributions of performance index by locations from each other. Theshape distribution of the second scatterers NS2 provided in the firstlayer LA1 and the shape distribution of the third scatterers NS3provided in the second layer LA2 may be determined such that degree ofnon-uniformity of focusing performance by the respective shapedistributions are different from each other. The shape distribution ofthe second scatterers NS2 provided in the first layer LA1 and the shapedistribution of the third scatterers NS3 provided in the second layerLA2 may be determined such that degree of non-uniformity of focusingperformance by locations in each layer may be compensated by each other.Any one of the first layer LA1 and the second layer LA2 may be set toalleviate the non-uniformity of focusing performance by the other layer.

As in the embodiment, when the scatterers are arranged in multiplelayers in the second thin lens 1301, the number of “27 zones” to which arule of a predetermined unit is applied may be reduced. The number of 2πzones R₁, R₂, . . . , R_(k), . . . , R_(N) as illustrated in FIG. 25 maybe set to a level appropriate to achieve a desired refractive power, andthe number of the regions increases for high refractive power. By usingthe multilayer arrangement, the number of regions formed in a radialdirection may be reduced.

Although the number of multiple layers is set to, for example, two, thepresent disclosure is not limited thereto. For example, three or morelayers may be selected. When the number of multiple layers is LN, thenumber of 2π zones formed in the radial direction may be reduced to1/LN. Furthermore, the dispersion range may be reduced to 1/LN.

FIG. 32 is a diagram of a focusing device 1002 according to anotherexemplary embodiment.

The focusing device 1002 may include the substrate 110, the first thinlens 1200 including the first scatterers NS1 formed on the first surfaceS1 of the substrate 110, and a second thin lens 1302 including aplurality of scatterers formed on the second surface S2 of the substrate110 and arranged in a two layer structure.

In the present embodiment, at least two of the second scatterers NS2forming the first layer LA1 of the second thin lens 1302 may havedifferent heights from each other. Furthermore, at least two of thethird scatterers NS3 forming the second layer LA2 of the second thinlens 1302 may have different heights from each other. As described inthe embodiment of FIG. 24, by applying height variation to each layer, adesign value to implement appropriate phase and dispersion at eachposition may be easy. In particular, when the multilayer scattererarrangement is introduced to compensate for the deterioration ofperformance of each layer, the selection of a design value of ascatterer to mutually compensate for the deterioration of performance ofone layer in another layer corresponding to a low correlation positionmay be easier. Furthermore, effective compensation of the phase and thedispersion performance between layers may be possible.

Although the drawing illustrates that the second and third scatterersNS2 and NS3 having various heights are applied to both of the firstlayer LA1 and the second layer LA2, this is merely exemplary and thepresent disclosure is not limited thereto. For example, the scatterersmay be arranged with a constant height in one of the first layer LA1 andthe second layer LA2, and the scatterers having a different height maybe selected in the other layer at an appropriately position asnecessary.

FIG. 33 is a diagram of a focusing device 1003 according to anotherexemplary embodiment.

Referring to FIG. 33, the focusing device 1003 may include the substrate110, a first thin lens 1201 including the first scatterers NS1 formed onthe first surface S1 of the substrate 110, and a second thin lens 1303including the second scatterers NS2 formed on the second surface S2 ofthe substrate 110.

The first scatterers NS1 of the first thin lens 1201 may be configuredto correct geometric aberration of the second thin lens 1303, and thesecond scatterers NS2 may be configured such that in the second thinlens 1303 may function as a lens with positive refractive power.

In the present embodiment, at least two of the first scatterers NS1 ofthe first thin lens 1201 may have different heights H from each other.The height difference ΔH of at least two first scatterers NS1 may beequal to or less than 2λ with respect to wavelength λ in the focusingwavelength band. The height H of the first scatterers NS1 may be in arange that λ/2≤H≤3λ, with respect to the wavelength λ of the focusingwavelength band.

As described above, the geometric aberration signifies a phenomenon thatlight incident in a direction that is not parallel to the optical axisof the focusing device 1003 is not focused on one focusing point. Thegeometric aberration of the second thin lens 1303 may be corrected bysetting the shape distribution of the first scatterers NS1 in the firstthin lens 1201. A target phase to be implemented by locations may be setfor the correction of geometric aberration. To achieve the target phase,the effect of correcting geometric aberration may be increased byselecting various heights of the first scatterers NS1.

FIG. 34 is a diagram of a focusing device 1004 according to anotherexemplary embodiment.

Referring to FIG. 34, the focusing device 1004 may include the substrate110, a first thin lens 1204 including a plurality of scatterers arrangedin a double layer structure on the first surface S1 of the substrate110, and the second thin lens 1302 including a plurality of scatterersarranged in a double layer structure on the second surface S2 of thesubstrate 110.

The first thin lens 1204 may include the first scatterers NS1 arrangedon the first surface S1 of the substrate 110, the low refractive indexmaterial layer 190 covering the first scatterers NS1 and including amaterial having a refractive index lower than the refractive index ofthe first scatterers NS1, and a plurality of fourth scatterers NS4arranged on the low refractive index material layer 190 and including amaterial having a refractive index higher than the refractive index ofthe low refractive index material layer 190. Furthermore, a lowrefractive index material layer 195 having a refractive index lower thanthe refractive index of the fourth scatterers NS4 may be furtherprovided to cover and protect the fourth scatterers NS4.

The second thin lens 1302 may include the second scatterers NS2 arrangedon the second surface S2 of the substrate 110, the low refractive indexmaterial layer 180 covering the second scatterers NS2, and the thirdscatterers NS3 arranged on the low refractive index material layer 180.Furthermore, the low refractive index material layer 185 having arefractive index lower than the refractive index of the third scatterersNS3 may be further provided to cover and protect the third scatterersNS3.

In the present embodiment, the scatterers are arranged in a double layerstructure on each of the first thin lens 1204 for correcting geometricaberration and the second thin lens 1302 for focusing light of apredetermined wavelength band with less color dispersion. Differentheights may be applied to the first scatterers NS1, the fourthscatterers NS4, the second scatterers NS2, and the third scatterers NS3,which form the respective layers.

Although, in the drawing, the scatterer arrangement of a multi-layeredstructure is applied to both of the first thin lens 1204 and the secondthin lens 1302 and height variation is applied to all layers, this ismerely exemplary and the present disclosure is not limited thereto. Forthe aberration correction and focusing effect suitable for each lens, anappropriate combination of multilayer arrangement and height variationmay be selected to mutually compensate for the performance deteriorationof each layer and extend the phase-dispersion map including design datato be selected therefor.

Although the two thin lenses included in each of the above-describedembodiments are formed on both sides of the substrate 110, this ismerely exemplary. For example, the two thin lenses may be formed ondifferent substrates and fixed such that an appropriate intervaltherebetween may be maintained by a predetermined support member.

It should be understood that exemplary embodiments described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exemplaryembodiment should typically be considered as available for other similarfeatures or aspects in other exemplary embodiments.

While one or more exemplary embodiments have been described withreference to the figures, it will be understood by those of ordinaryskill in the art that various changes in form and details may be madetherein without departing from the spirit and scope as defined by thefollowing claims.

What is claimed is:
 1. A focusing device with respect to light of apredetermined wavelength band, the focusing device comprising: asubstrate; a first thin lens provided at a first surface of thesubstrate and comprising a plurality of first scatterers; and a secondthin lens provided at a second surface of the substrate and comprising aplurality of second scatterers, wherein the plurality of firstscatterers of the first thin lens are configured to correct geometricaberration of the second thin lens, and wherein at least two of theplurality of second scatterers have different heights from each other.2. The focusing device of claim 1, wherein a height difference betweenthe at least two second scatterers is equal to or less than 2λ withrespect to a wavelength λ within the predetermined wavelength band. 3.The focusing device of claim 1, wherein a height H of the plurality ofsecond scatterers is in a range that λ/2≤H≤3λ, with respect to awavelength λ within the predetermined wavelength band.
 4. The focusingdevice of claim 1, wherein the second thin lens further comprises: a lowrefractive index material layer covering the plurality of secondscatterers and including a material having a refractive index lower thana refractive index of the plurality of second scatterers; and aplurality of third scatterers arranged on the low refractive indexmaterial layer and including a material having a refractive index higherthan a refractive index of the low refractive index material layer. 5.The focusing device of claim 4, wherein the plurality of secondscatterers and the plurality of third scatterers face each other to bemisaligned with each other.
 6. The focusing device of claim 4, wherein aseparation distance in a height direction between adjacent second andthird scatterers among the plurality of second scatterers and theplurality of third scatterers is greater than λ/2, with respect to thewavelength λ within the predetermined wavelength band.
 7. The focusingdevice of claim 4, wherein a shape distribution of the plurality ofsecond scatterers and a shape distribution of the plurality of thirdscatterers are determined to have different distributions of performanceindexes by locations from each other.
 8. The focusing device of claim 7,wherein the shape distribution of the plurality of second scatterers andthe shape distribution of the plurality of third scatterers aredetermined to mutually compensate for non-uniformity in focusingperformance by locations.
 9. The focusing device of claim 4, wherein atleast two of the plurality of third scatterers have different heightsfrom each other.
 10. The focusing device of claim 9, wherein a heightdifference between at least two of the plurality of third scatterers isequal to or less than 2λ, with respect to the wavelength λ within thepredetermined wavelength band.
 11. The focusing device of claim 4,wherein a height H of a plurality of fourth scatterers is in a rangethat λ/2≤H≤3λ, with respect to the wavelength λ within the predeterminedwavelength band.
 12. The focusing device of claim 1, wherein at leasttwo of the plurality of first scatterers have different heights fromeach other.
 13. The focusing device of claim 1, wherein the first thinlens further comprises: a low refractive index material layer coveringthe plurality of first scatterers and including a material having arefractive index lower than a refractive index of the first scatterer;and a plurality of fourth scatterers arranged on the low refractiveindex material layer and including a material having a refractive indexhigher than a refractive index of the low refractive index materiallayer.
 14. The focusing device of claim 13, wherein the plurality offirst scatterers and the plurality of fourth scatterers face each otherto be misaligned with each other.
 15. The focusing device of claim 13,wherein a separation distance in a height direction between adjacentfirst and fourth scatterers among the plurality of first scatterers andthe plurality of fourth scatterers is equal to or less than λ/2, withrespect to the wavelength λ within the predetermined wavelength band.16. The focusing device of claim 1, wherein the first and the secondthin lenses are configured to allow light to form a focusing point on afocal plane.
 17. The focusing device of claim 1, wherein a phase shiftof light that passes through the plurality of second scatterersdecreases from a central area of the second thin lens to a peripheralarea of the second thin lens.
 18. The focusing device of claim 17,wherein a phase shift of light that passes through the plurality offirst scatterers decreases from a peripheral area of the first thin lensto a middle area of the first thin lens and increases from the middlearea of the first thin lens to a central area of the first thin lens.19. The focusing device of claim 16, wherein the first and the secondthin lenses are configured to change a location of the focusing pointaccording to an angle at which the light is incident on the firstsurface.
 20. The focusing device of claim 19, wherein the first and thesecond thin lenses area configured to determine the location of thefocusing point according to Equation 1:h=f*tan θ wherein ‘h’ is a distance between the location of the focusingpoint and an optical axis of the focusing device, ‘f’ is an effectivefocal length of the focusing device, and ‘θ’ is the angle at which thelight is incident on the first surface.